THIS WEEK MARKS two milestones for the Harvard Cooperative Society. Both should serve to remind Coop officials of its responsibilities to Harvard and MIT students--the Coop's principal shareholders--and especially to its own employees.

When the Coop begins its second century tomorrow, it celebrates a tradition of communal service, one that began in 1882 when Harvard students united to beat the high prices of textbooks and firewood. But ironically, the Coop of 1982 seems more a monopoly than a cooperative. Its vast expansion into Boston markets, in which few students participate, has helped deprive students of the membership control that was once a hallmark of the Coop.

Indeed, the very ideal of the cooperative seems to have disappeared, submerged by a Coop management more intent on expansion than cooperation with its student members. Last year's progressive Coop Group slate ran on--and won-student directorships on a platform of higher employee wages and benefits, better working conditions, and more equitable pricing policies. Once elected, many worked hard for those goals, and did manage to extract some data from Coop management. But that was all.

The student directors increasingly realized the near-impossibility of accomplishing real change in a tightfisted, multimillion dollar company. And if the active and well-intentioned Coop Group could effect no change, it's hard to see how any student "members" could.

The Coop's second red-letter event this week calls to mind other questionable policies, these ones concerning Coop employees. Monday, the National Labor Relations Board heard the Coop defend itself against the board's charges that Coop management illegally interfered with an unsuccessful unionization drive last year--that it employed a variety of union-busting techniques to quash a union that sought to improve wages and working conditions. Whether or not those allegations are accurate, they suggest more fundamental labor problems.

The transient character of Harvard Square labor has allowed the Coop to pay its workers often shockingly low wages, scarcely above the minimum wage for some full-time stockboys and clerks. The plight of older Coop workers is often worse. Forced to cope with high inflation, they can find little comfort in the Coop's low wages. Employees have cited other labor problems: oppressive monitoring, inconsiderate assignment of tasks, and biased promotion procedures.

At a time when Coop rebates are running close to 10 percent--and when additional profits are being funneled into expansion--maintaining low wages and benefits seems particularly reprehensible. The Coop--led by its student directors--should try to improve wages and benefits and institute a regular policy of rechanneling half of member rebates back into employee benefits, where they will do far more good.

For Coop management, then, the store's 100th anniversary should be occasion not for placid celebration--for profits alone are nothing to celebrate--but instead for looking both back at the Coop's past and ahead to its future. The past should remind them of the forgotten ideals of the retail cooperative--fair prices, compassionate treatment of workers, and cooperation with its membership. The future, we hope, will allow the Coop to realize those ideals better than it has in recent years.